1. Field of the Invention
The present invention relates to an optical exposure technique of exposing a mask and a wafer to a radiation beam, such as a synchrotron radiation beam or the like, so as to transfer a mask pattern onto the wafer.
2. Description of the Related Art
Conventionally, in an optical exposure process employed whereby a mask and a wafer are exposed to light so as to transfer a mask pattern formed on the mask to the wafer, the temperature of a wafer chuck for holding the wafer by suction is changed to extend or contract the wafer, thereby performing the correction of the magnification. However, in the proximity exposure method through the use of an X-ray having a shorter wavelength, an X-ray transmission film of the X-ray mask having a pattern to be transferred formed thereon is held on the wafer with only a small gap of several dozens of .mu.m. Also, the X-ray mask has a small specific heat. Consequently, a change in the temperature of the wafer entails a change in the temperature of the mask, which further unavoidably causes the extension or the contraction of the mask.
In order to overcome the above-described drawback, the following method of correcting the transfer magnification has been suggested. That is, a gap between the mask and the wafer (a proximity gap) is relatively changed, or alternatively, the temperature of the wafer or the mask is varied.
The following three types of exposure methods of performing the scanning exposure are known in the lithographic technology by use of a synchrotron radiation beam.
(1) An X-ray mirror is rocked (rotated) to allow a sheet beam-like synchrotron radiation beam to undergo deviation. PA1 (2) A mask and a wafer are integrally moved in relation to a sheet beam which is fixed to be oriented. PA1 (3) A shutter having a predetermined-width opening is moved in relation to a divergent beam which is fixed to be oriented.
However, whichever method is employed, there is a difference in the divergent angle of the beam between the scanning direction (Y direction) and the direction orthogonal thereto (X direction), disadvantageously resulting in a disparity in the transfer magnification between the X and Y directions. Further, when the synchrotron radiation beam is converged in the X direction through the use of a convergent optical system, a difference in the diverging angle of the beam is produced between the X and Y directions, also resulting in a disparity in the transfer magnification between the X and Y directions.
Because of the above-described problem, the separate correction of the magnification in the X and Y directions cannot be achieved merely by changing the proximity gap or the temperature of the wafer or the mask, thus failing to correct a disparity in the magnification between the X and Y directions.